To add to the above, most every residents has two wires(plus ground) coming into the house, half the devices in the house come off circuit breakers hooked one side and half to the other. Things like larger air conditioners, large air compressors, electric stoves or large permanent(hard wired) heaters will be hooked up to both hots to get 240. Of course we are 60hz ac while most of the rest of the world is 50hz ac.
A typical house will have 30+ 120v breakers and a few 240v breakers, most 120v breakers are 15 or 20 amps(14 or 12 gauge copper wiring). 110v and 120v(or 220v/240v) are one in the same, most power is closer to the 120v.